6m crank in my 7m!

[2543arvin]

well, i finished tearing my jdm motor apart and guess what i found? A 6m crank in my 7mgte! The whole bottom end had been rebuilt, except for the pistons. The rods were peened, bearings replaced, new oil pump, and a 6m crank. Im guessing that my jdm motor wasnt daily driven by its original owner, so my question(s) are.....Is the 6m crank a better option? And if so, will my wisecos and eagle rods i already have fit on the 6m crank? And what about the bearings, will they be the same? I tried searching and all i found were build threads, so sorry if this is a repost. Thanks for the help!

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sorry for the blurry pic, but i think it gets the point across

 

[supradan22]

6m cranks came in pre 89 bottom ends there not as heavy as the 7m cranks but the 7m cranks are ballanced and smoother at redline.

All your new parts will work on the 6m crank fine.

 

[2543arvin]

well, either way the crank will be balanced, so will that help at redline? sorry for the stupid questions but i defintiely didnt plan on finding a 6m crank in my jdm motor

 

[supradan22]

Yeah it'll make things smoother at redline the 7m crank has weights on it that ballance it

Top 7M crank Bottom 6M

Quoted IJ from my build thread.

 

[2543arvin]

Yeah it'll make things smoother at redline the 7m crank has weights on it that ballance it



Quoted IJ from my build thread.

thanks man for the help

 

[Dirgle]

Here's a good simple post on the differences.

http://www.supramania.com/forums/showpost.php?p=87227&postcount=2

And multiple users have mentioned that even after balancing the 7M crank is smoother than the 6M. Probably because the best balancing in the world can't account for missing counter weights on cylinder #2 and #5

 

[starscream5000]

^ I though something didn't look quite right with the #2 and #5's on the 6M .

 

[MK3.0dudeman]

damn i wish i had a 89+

 

[jdub]

Early '89's had the 6M crank as well
Seen a couple in later models too...either Toyota simply used up the 6M crank supply or the car did not have the original motor.

The 6M crank will balance out nicely, especially if it's lightened up a bit....but, the 7M is smoother with the same treatment...no doubt.

 

[AF1JZ]

The gte engine that came out of my 89+ had a 6m crank in it. Didn't even think about it at the time till now. Interesting. I went 1jz though, so it doesn't matter.

 

[Jeff Lange]

ALL 89 cars had the 6M crank.
All 90+ cars had the 7M crank.

Different part numbers, and both are still available, so using up supply obviously wasn't the point or the 6M part would be gone.

 

[CRE]

So Jeff, what's MSRP for a 7M crank?

 

[Jeff Lange]

$921.60

 

[Nick M]

Do you know what would happen if the number 2 and 5 had no counter weight anywhere?